this was exactly what he was doing
we played two matches and all he did was play Mii gunner and only use four moves: Side B, B, Roll, and side A
do you know how predictable using those four moves are
just dodge the side b, take advantage of the cooldown and use a smash attack/tilt
if you think he'll roll use a projectile/dash attack/slide smash (basically, as soon as you start dashing input an up smash command
if you think he'll use neutral B or side A use a counterattack (includes reflect and absorption attacks)